Scenedesmus Obliquus Research Articles

Cultivation of microalgae Chlorella vulgaris, Monoraphidium sp and Scenedesmus obliquus in wastewater from the household appliance industry for bioremediation and biofuel production.

Microalgae Chlorella vulgaris, Scenedesmus obliquus, and Monoraphidium sp were cultivated in effluent from the household appliance industry as an alternative medium for bioremediation due to the high variability of chemical and biological substances in wastewater. The experiments were carried out using biological effluent (BE), chemical effluent (CE), and a combination of the two (MIX). The results showed a maximum biomass yield of 1056mg/L (± 0.216) in the BE cultivation of the microalga Scenedesmus obliquus, 969mg/L (± 0.20) in the BE of the microalga Monoraphidium sp. and 468mg/L (± 0.46) in the CE of Chlorella vulgaris. In addition, they showed removal (100%) in the CE and MIX for cultivation with Chlorella vulgaris and 100% BE and 75% MIX with Monoraphidium sp. For the (75.3%, 99% e 97.9%) in the cultures with C. vulgaris BE, CE, and MIX respectively, with Monoraphidium sp. 58% in BE and 42% in CE and MIX. With S. obliquus, 100% removal was observed in all 3 treatments. Metal removal was also observed. The C. vulgaris culture showed lipid contents of 16%, 12%, and 17% for BE, CE, and MIX, respectively. For Monoraphidium sp., 14.5% for BE, 16% for CE, and 14% for MIX. In the culture of S. obliquus, 17%, 15.5%, and 16.5% for BE, CE, and MIX, respectively.

Effects of Toxic and Non-Toxic Microcystis aeruginosa on the Defense System of Ceratophyllum demersum–Scenedesmus obliquus

The effects of toxic and non-toxic Microcystis aeruginosa on the Ceratophyllum demersum–Scenedesmus obliquus system were simulated in the laboratory, and some parameters in relation to these organisms were measured. In this experiment, C. demersum increased the biomass of S. obliquus, and both toxic and non-toxic M. aeruginosa significantly inhibited the colony formation of S. obliquus and inhibited the promotion of S. obliquus biomass. On the 14th day, the soluble polysaccharide content of C. demersum decreased when it was coexisted with S. obliquus, but it rose again because of M. aeruginosa, which significantly increased the protein content of C. demersum. The species composition and diversity of epiphytic microorganisms also vary with different treatments. Proteobacteria is dominant in all the groups, especially in the Toxic_SMC group. In addition, bacteria that can degrade organic pollutants are more abundant in Toxic_SMC group. This study focuses on the defense response of S. obliquus induced by C. demersum under the pressure of toxic or non-toxic M. aeruginosa and evaluates the changes to C. demersum and its epiphytic microorganisms, which provides insights for the study of aquatic plant–algae integrated action systems in eutrophic or cyanobacterial blooms.

A comparison of biofilm and suspension methods in removing heavy metals (chromium) from industrial wastewater with Scenedesmus obliquus and Chlorella vulgaris

The study investigated the factors influencing chromium absorption by the microalgae species S. obliquus and C. vulgaris using an ANOVA approach. The analysis revealed significant independent effects of contact time, temperature, pH, density, algal species, and production methods, as well as notable interactions among these factors. Under standardized conditions of pH 7, 105 minutes of contact time, a temperature of 25°C, light intensity of 3500 lux, and a density of 60, S. obliquus showed the highest chromium absorption. The biofilm production method was consistently more effective than the suspension method for both species. At a pH of 5, C. vulgaris outperformed S. obliquus, achieving maximum absorption rates in both production methods. The study also found that higher temperatures facilitated increased chromium absorption, peaking at 27.5°C for suspension and 26.5°C for biofilm methods, with S. obliquus demonstrating superiority. Significant interactions resulted in the combination of the biofilm method and S. obliquus yielding the best absorption rates at specified conditions. Density trends indicated decreasing absorption rates for both microalgae at densities of 30 and 40, but S. obliquus later exhibited a reversal of this trend, unlike C. vulgaris. Contact time results indicated increased absorption from 60 to 115 minutes, but a decline afterwards, with S. obliquus again leading. The optimal conditions for chromium absorption were identified as pH 5, temperatures around 26–28°C, with particular density levels, highlighting the importance of production method in enhancing absorption rates for both microalgae species.

Effects of acetochlor on the interaction between Scenedesmus and Microcystis: Integrated perspectives on toxicity, biotransformation, and competition strategies

To reveal the disruption caused by herbicides and the mechanisms of algal interactions on interspecific competitive strategies at a metabolic and population level, this study established short-term (7 d) and long-term (21 d) Scenedesmus–Microcystis competition coculture systems and investigated the toxicity of acetochlor (ACT) on algae competition. Scenedesmus obliquus (EC50 6.586μg/L) is three orders of magnitude more sensitive to ACT than Microcystis aeruginosa (EC50 19,539μg/L), placing it at a competitive disadvantage in environments with ACT pollution. Short-term coculture tests (ACT concentrations from 0 to 12.5μg/L) showed that ACT suppresses S. obliquus growth and competition, while M. aeruginosa initially showed compensatory growth, which was negated by ACT. Metabolomics revealed that interspecies competition and ACT affect fatty acid synthesis and nitrogen assimilation metabolism of both microalgae, suggesting species differences in the mode of action (MOA) of ACT toxicity and resource competition strategies, respectively. ACT weakens the ability of M. aeruginosa to compete for nitrogen and synthesize microcystin under competitive stress. ACT biotransformation can be conducted across species. In an algal culture system with equal initial biomass, the 7 d ACT degradation rate increased by 24.9% and 123.8% with coculture of the two algae compared with monocultures of S. obliquus and M. aeruginosa, respectively. In long-term experiments, the degradation rate increased by 19.0% and 8.9% in cocultures compared with the monocultures. Lotka–Volterra models showed that competitive inhabitation was alleviated, implying that the competition interspecies relationship is beneficial for the coexistence of both algal populations under ACT stress.

Trophic transfer of carbon-14 from algae to zebrafish lead its blending in biomolecules and dysregulating metabolism via isotope effect

Abstract Carbon-14 (C-14) has been a major contributor to the human radioactive exposure dose, as discharged into environment from nuclear industry in larger quantities compared to other radionuclides. This most abundant nuclide enters the biospheric lifecycle as organically bounded C-14 (OBC-14) and threatens to public health, yet it remains unknown how this low radiotoxic nuclide induces health risks via chemical effects, e.g. isotope effect. Via establishing trophic transfer model by algae (Scenedesmus obliquus), daphnia (Daphnia magna) and zebrafish (Danio Rerio), we show that, rapidly incorporation and transformation of inorganic C-14 by algae into OBC-14 enables the blending of C-14 in biomolecules of zebrafish. We find that internalized C-14 persistently retains in brain of zebrafish, impacting on DNA methylation and inducing neuropathology alteration. Global isotope tracing metabolomics with C-14 exposure further highlight the participation of C-14 in various critical metabolic pathways, including one-carbon metabolism and nucleotide metabolism. We thus characterize the kinetic isotope effects (KIEs) for 12C/14C in the critical reaction of this metabolism via kinetic experiments and density functional theory (DFT) computations, showing that the isotopically substitution of carbon in biochemicals regulate metabolism by disrupting reaction ratios via isotope effect. Our findings suggest that nuclear industry discharged inorganic C-14 can be biotransformed to be organically bounded with biomolecules to impact metabolisms via isotope effect, providing new insights on understanding the health risk of C-14 that supposed to be a low radiotoxic nuclide.

Integrating electrochemical pretreatment with microalgae treatment for nitrogen and phosphorus removal and resource recovery from swine wastewater

This study integrates electrochemical pretreatment with microalgae (Scenedesmus obliquus) treatment to enhance nitrogen and phosphorus removal and resource recovery from swine wastewater. By optimizing electrochemical and microalgae treatment conditions, the dilution factor and the hydraulic retention time for microalgae treatment were reduced to 5 times and 7 days, respectively. Under the optimized operational conditions, removal efficiencies of total nitrogen and ammonia could reach over 89 %and 96 %,respectively, and the removal efficiency of total phosphorus was over 99 %. The study also found that aluminum was more suitable than iron for anode as it produced fewer residues. Additionally, the electrochemical pretreatment reduced Cu2+ and Zn2+ concentrations, mitigating negative impacts on microalgal growth. The microalgae biomass harvested from developed processes was rich in saturated fatty acids, which was desirable for biodiesel production. This approach addresses the challenges of nutrient removal for swine wastewater treatment with high quality biomass recovery.

Polystyrene microplastics enhanced the photo-degradation and -ammonification of algae-derived dissolved organic matters

Algae-derived organic matter (ADOM) is a key source of chromophoric dissolved organic matter (CDOM) in natural waters. When exposed to solar irradiation, ADOM undergoes gradual degradation and transformation. The escalating presence of microplastics (MPs) can act as a novel type of environmental photosensitizer, however its impacts on ADOM photodegradation remains largely unexplored. Thus, in this study, ADOM were extracted from four common algal species (Microcystis aeruginosa, Synechococcus sp., Chlorella pyrenoidosa and Scenedesmus obliquus) and exposed to UV irradiation with or without polystyrene (PS) MPs, namely ADOM+PS groups and ADOM groups, respectively. The results indicated that a more rapid degradation of amino acid-like substances (∼38 % vs. ∼22 %) and more ammonia products (1.86 vs. 1.21 mg L−1) were observed in the ADOM+PS groups compared to the ADOM groups after a five-day exposure. This enhanced photodegradation might be attributed to the production of environmentally persistent free radicals and reactive species during the photoaging of PS. Furthermore, PS-derived high electron transfer belt activity of ADOM led to the production of highly aromatic and humified products. These humic-like products could potentially accelerate the degradation of amino acid-like compounds by exciting the generation of excited triplet CDOM. This study underscores the role of MPs as environmental photosensitizers in promoting ADOM degradation and ammonia generation, providing insights on the transformation of ADOM mediated by emerging pollutants and its impact on aquatic carbon and nitrogen cycles.

Optimization of the alcalase and trypsin hydrolysis conditions of an isolated protein from Scenedesmus obliquus microalgae and characterization of its functional properties

This study focused on fine-tuning the enzymatic hydrolysis variables, specifically the duration and enzyme concentrations of alcalase and trypsin, for Scenedesmus obliquus protein using response surface methodology (RSM) with a central composite design (CCD). The aim was to characterize the amino acids, separate hydrolysates based on molecular weight, and assess functional activities such as antioxidant, emulsifying, fat-binding, and foaming capacities. After fractionating the hydrolysates, bioactivities were evaluated through standard assays. The optimal hydrolysis conditions—10.24 g/100 mL alcalase and 2.56 g/100 mL trypsin—yielded the highest protein extraction. Peptides smaller than 5 kDa demonstrated 80% DPPH inhibition and superior fat-binding capacity. Emulsifying capacity peaked at 112 m2/g for peptides under 10 kDa, and the highest foaming index was observed for peptides below 5 kDa. The application of RSM effectively optimized the hydrolysis of microalgal protein isolates for maximum efficiency, highlighting microalgae's potential as a sustainable source of functional ingredients.

Lipid content and wastewater treatment potential of Chlorella vulgaris and Scenedesmus obliquus isolated from Uzuncayır Dam Lake

Production of microalgae for biodiesel, one of the alternative renewable energy sources, is costly due to nutrient media. Industrial and domestic wastewater contains nitrogen, phosphorus and other nutrients that are the primary food source for algae. Releasing this environmentally harmful effluent into receiving bodies of water, such as the sea or a freshwater reservoir, without prior treatment causes serious problems. Combining microalgae cultivation with wastewater treatment is a promising strategy for improving wastewater and reducing the cost of nutrient media required for algae production. In this study, wastewater obtained from a wastewater treatment facility was diluted with clean water to 0.25%, 50%, and 75% concentrations, and Chlorella vulgaris and Scenedesmus obliquus were cultured in these nutrient media for 20 days. As a result, microalgae increased their biomass and lipid content, while consuming nitrite, nitrate, phosphate, and ammonium from the wastewater as nutrients.

Waste-recovered quaternary blends: Enhancing engine performance through hydrogen induction by varied injection timing and pressure for sustainable practices

This study explores sustainable energy solutions by utilizing waste-recovered quaternary blends of Scenedesmus obliquus, waste plastics, n-octanol, and hydrogen induction to enhance engine performance. This research aims to address this imperative by proposing a novel blend that not only repurposes waste materials but also leverages hydrogen induction to augment the combustion characteristics of a single cylinder Kirloskar engine's injection timing and injection pressure. The waste plastic is recovered by the pyrolysis method and Scenedesmus obliquus by the transesterification process. The study revealed that out of all the blends, the fuel at 23° before Top Dead Center (bTDC) and 210 bar outperformed all blends with 1.99% better brake thermal efficiency than diesel. The lowest brake specific energy consumption observed was 10.753.35 MJ/kW-hr at 23° bTDC and 240 bar injection pressure, which was 160.38 kJ/kW-hr higher than diesel. Fuel Injection Timing at 23° bTDC at 170 bar shows a 42 ppm decrease for Scenedesmus Obliquus Waste Plastic Octanol 50% (SOWPOCT50) mix compared to diesel. At fuel injection timing (FIT) timing, 23° bTDC and a pressure of 240 bar Injection Pressure (IP), the SOWPOCT50 mixture lowered 0.097 g/h Carbon Monoxide (CO) concentration to diesel. This enormous increase in efficiency and reduction in emission paved a potential replacement source for neat diesel towards the Sustainable Development Goals.

Assessing ecotoxicity, removal efficiency, and molecular response of freshwater microalgae to bisphenol AP

Bisphenol AP (BPAP), an analog of BPA and endocrine disrupter, is increasingly being detected in water, signaling its rise as an environmental contaminant similar to BPA, which is known for its health implications. This study investigated the ecotoxicity of BPAP in four freshwater microalgae (Chlorella sorokiniana, Chlamydomonas mexicana, Scenedesmus obliquus, and Chlorella vulgaris), along with their removal potential and biotransformation. This was followed by de novo transcriptomic analysis to elucidate the molecular response after BPAP exposure. The toxicity (120 h-EC50) of BPAP for microalgal species ranged from 1.509 mg L−1 to 6.509 mg L−1. C. mexicana exhibited the highest removal efficiency of 86.5 % after 12 days, followed by C. vulgaris (86.0 %), S. obliquus (78.9 %), and C. Sorokiniana (56.5 %) at 1 mg L−1. Eight biotransformed BPAP products were analyzed, and their toxicity was predicted to be lower than that of BPAP using the Ecological Structure Activity Relationships software. Transcriptomic analysis of C. mexicana revealed the differential expression of 4611 genes in processes related to metabolism, cellular activities, and stress responses. Genes encoding methyltransferases, glycosyltransferases, and various oxidoreductases, including electron-transferring flavoprotein dehydrogenase and glutaredoxin, were significantly upregulated in algal cells exposed to BPAP, suggesting the potential of C. mexicana for BPAP detoxification via glycosylation and transmethylation. These results offer novel insights into the ecotoxicity, removal potential, and biotransformation of BPAP in freshwater microalgae, with transcriptomic analysis, elucidating the molecular mechanisms of BPAP detoxification for effective environmental remediation.

Optimization of Culture Conditions for Microalgae Treatment Fly Ash Leachate System

In order to explore the feasibility of using algae to treat the fly ash leachate from a safe landfill site, leachate samples taken from a certain safe landfill site in Wenzhou City were treated with two different microalgae, Chlorella vulgaris and Scenedesmus obliquus, and the effectiveness of each treatment was evaluated in terms of its efficiency of pollutant removal. The effects of conditions such as pretreatment of leachate by sterilization, the initial concentration of leachate, and the addition of nutrients on pollutant removal efficiency and algae growth were studied. Sterilization of the leachate was found to have a relatively small impact on the growth of C. vulgaris and S. obliquus, as well as the removal of pollutants from the leachate. Therefore, sterilization treatment may not be necessary for engineering applications. Algal growth and the removal of pollutants were optimal when the leachate was used at a concentration of 10%, but when the leachate concentration was 30% or higher, the growth of both algae was weakened. The inclusion of 0.2 g/L K2HPO4·3H2O and 0.06 g/L ammonium ferric citrate in the system led to higher algal growth and pollutant removal. The chlorophyll a levels of C. vulgaris and S. obliquus were 555.53% and 265.15%, respectively, and the nitrogen removal rates were also the highest, reaching 59.51% and 56.69%, respectively. This study optimized the cultivation conditions of a microalgae treatment leachate system, providing technical support and a theoretical basis for the practical engineering of a harmless treatment of leachate.

Terahertz spectroscopy-based rapid detection of exchangeable heavy metal pollution in soil using Scenedesmus obliquus

This study introduces a novel approach for the rapid detection of exchangeable heavy metal pollution in soil, utilizing Scenedesmus obliquus as a bioadsorbent. Terahertz spectroscopy was used to analyze the cell wall proteins and functional groups of S. obliquus following physical adsorption. This analysis enabled the deduction of the types and concentrations of exchangeable heavy metal ions in soil. We established a prediction model for heavy metal concentrations using partial least squares (PLS) regression, achieving optimal detection times: 10 min for Pb2+, 20 min for Ni2+, and 30 min for Co2+. Validation with real surface soil samples demonstrated excellent accuracy rates: 97.8 % for Pb2+, 91.8 % for Ni2+, and 90 % for Co2+. Notably, our method reduces the detection time to 0.5 hours, requires only 5 ml of sample volume, and enhances detection accuracy to 0.1 μg/L.

Simultaneous organic wastewater treatment and bioelectricity production in a dual chamber microbial fuel cell with Scenedesmus obliquus biocathode

Algal biocathode MFCs (ABMs) are recently being heavily studied due to their advantage over abiotic cathode MFCs (ACMs) as dissolved oxygen (DO) generated by algal growth in the cathodic chamber is directly utilized in cathodic oxidant reduction. In this work growth of pure algae species Scenedesmus obliquus used in the cathode chamber has been studied under a photoperiod of 24 h illumination to supplement oxygen for continual MFC operation without any external supply of air or carbon dioxide and treatment of synthetic wastewater having chemical oxygen demand (COD) equivalent to medium strength domestic wastewater (5.35 g/L COD). Results of ABM showed the highest continuous current density generation of 23.93 mA/m2 and the highest continuous volumetric power density generation of 13.24 mW/m3 were around 120 h with COD removal efficiency of 92.52 % and coulombic efficiency (CE) of 41.88 %. Initial ohmic (Roh) and charge transfer (Rct) resistance values of ABM were found to be 8.3 Ω and Rct of 22.5 Ω which after 216 h of algal growth got reduced to 1 Ω and 15.1 Ω respectively. 16S microbiome profiling of the mixed microbial sludge inoculum used in the anodic chamber showed dominance of Xanthomonadaceae stenotrophomonas (9.7 %), Chitinophaga flexibacter (8.65 %), Sphingomonadaceae sphingomonas (6.82 %), Sphingobacterium multivorum (6.55 %), Dyadobacter fermentans (6.05 %), and Alcaligenaceae achromobacter (5.51 %). Elemental investigation of the bioanode’s and biocathode’s surface carried out using EDS analysis also shows that oxygen was generated in the cathodic chamber by pure Scenedesmus obliquus species.

Effects of 17α-ethinyl estradiol (EE2) and removal potential by two microalgal species Chlorella vulgaris and Scenedesmus obliquus

17α-ethinyl estradiol (EE2) is the primary component in birth control pills and is highly bioavailable when taken orally. However, 80 % of the administrated dose is excreted un-metabolized in feces and urine, leading to its detection in water bodies and wastewater effluent from conventional treatment plants. EE2 negatively impacts on aquatic ecosystems, including disruption to the endocrine system of organisms, causing feminization in males, egg production and fertilization perturbation.Microalgae-based wastewater treatment is a promising biological approach for removing pollutants from the environment, including emergent and persistent contaminants. In this study, we evaluated the tolerance of two microalgal species Chlorella vulgaris (C. vulgaris) and Scenedesmus obliquus (S. obliquus) to various EE2 concentrations (0, 0.05, 0.10, 0.20, 0.30, 1.00, 8.0 and 22.0 mg L−1). Their potential to remove EE2 and the corresponding degradation kinetics were also assessed. The results showed that both species tolerated concentrations up to 8.0 mg EE2 L−1; however, at 22.0 mg EE2 L−1, C. vulgaris biomass decreased, and S. obliquus growth was inhibited. S. obliquus removed over 90 % of EE2 for most concentrations tested, while C. vulgaris achieved a maximum removal of 64 %. EE2 removal was attributed to microalgal biodegradation rather than sorption or bioaccumulation. The kinetic parameters determined that EE2 half-life was one day in S. obliquus culture and nine days in C. vulgaris. These findings confirmed that S. obliquus, especially, could reduce EE2 half-life in the environment, facilitating its removal. This information is valuable to understand EE2 degradation in aquatic ecosystems with microalgae presence.

Inhibitory effects of toxic Dolichospermum flos-aquae and anatoxin-a on inducible defenses of Daphnia magna

Cyanobacterial blooms, resulting from serious eutrophication, can produce various cyanotoxins and severely disrupt aquatic ecosystems. Inducible defenses are adaptive traits developed by prey in response to predation risks. However, the effects of the increasing proportion of cyanobacteria and cyanotoxins produced during cyanobacterial blooms on the inducible defenses of cladocerans, particularly in terms of behavioral defenses, remain unclear. In this study, we selected Daphnia magna and investigated the defensive traits against predation risks by the predator Rhodeus ocellatus under different ratios of cyanobacteria (Dolichospermum flos-aquae) and green algae (Scenedesmus obliquus), as well as varying concentrations of anatoxin-a (ATX), a cyanotoxin. We recorded the inducible defensive traits involving to morphology, behavior, and offspring production of D. magna. Results showed that the body length of D. magna at sexual maturity and the number of offspring in the first brood were significantly reduced by the presence of D. flos-aquae. Moreover, when the proportion of D. flos-aquae reached 75% and 100%, D. magna did not develop to sexual maturity. Furthermore, D. flos-aquae inhibited the formation of inducible behavioral defense of D. magna, with a stronger inhibitory effect as the proportion of D. flos-aquae increased. In this experiment, the effects of ATX on the morphological traits at sexual maturity and offspring production of D. magna were minor, but ATX still had the potential to inhibit the formation of inducible behavioral defense. We confirmed that changes in the proportion of cyanobacteria and green algae as well as the production of ATX by cyanobacteria during cyanobacterial blooms can affect the growth, development, and inducible defensive traits of cladocerans, potentially altering their population dynamics during such events.

Microplastics with different functional groups modulate cellular and molecular mechanisms of reduced graphene oxide toxicity on the green microalga, Scenedesmus obliquus

Even though microplastics (MPs) and graphene nanomaterials (GNMs) have demonstrated individual toxicity towards aquatic organisms, the knowledge gap lies in the lack of understanding regarding their combined toxicity. The difference between the combined toxicity of MPs and GNMs, in contrast to their individual toxicities, and furthermore, the elucidation of the mechanism of this combined toxicity are scientific questions that remain to be addressed. In this study, we examined the individual and combined toxicity of three polystyrene microplastics (MPs) with different functional groups—unmodified, carboxyl-modified (COOH-), and amino-modified (NH2-) MPs—in combination with reduced graphene oxide (RGO) on the freshwater microalga Scenedesmus obliquus. More importantly, we explored the cellular and molecular mechanisms responsible for the observed toxicity. The results indicated that the growth inhibition toxicity of RGO, either alone or in combination with the three MPs, against S. obliquus increased gradually with higher particle concentrations. The mitigating effect of MPs-NH2 on RGO-induced toxicity was most significant at a higher concentration, surpassing the effect of unmodified MPs. However, the MPs-COOH did not exhibit a substantial impact on the toxicity of RGO. Unmodified MPs and MPs-COOH aggravated the inhibition effects of RGO on the cell membrane integrity and oxidative stress-related biomarkers. Additionally, MPs-COOH exhibited a stronger inhibition effect on RGO-induced biomarkers compared to unmodified MPs. In contrast, the MPs-NH2 alleviated the inhibition effect of RGO on the biomarkers. Furthermore, the presence of differently functionalized MPs did not significantly affect RGO-induced oxidative stress and photosynthesis-related gene expression in S. obliquus, indicating a limited ability to modulate RGO genotoxicity at the molecular level. These findings can offer a more accurate understanding of the combined risks posed by these micro- and nano-materials and assist in designing more effective mitigation strategies.

Release kinetic study of microplastics from N95 face masks and consequent effects on freshwater alga Scenedesmus obliquus

The uncontrolled disposal of N95 face masks, widely used during the recent COVID-19 pandemic can release significant amounts of microplastics and other additives into aquatic bodies. This study aimed to: (i) to quantify and analyze the released microplastics and heavy metals from N95 face masks weathered for various time periods (24, 48, 72, 96, 120, and 144 h) and (ii) to assess the cytotoxicity potential of the leachates on a model organism, freshwater alga Scenedesmus obliquus. The mask leachates contained microplastics, polypropylene in different shapes and sizes, and heavy metals like Cu, Cd, and Zn. The leachates significantly reduced cell viability and increased reactive oxygen species (ROS) generation, antioxidant enzyme activity, and membrane damage. The effects were also accompanied by a significant drop in the photosynthetic yield. All of the examined parameters indicated a dose-response relationship, with longer leaching periods resulting in higher microplastic concentrations. Mask leachates severely damaged the structural integrity of the algal cells, as seen in scanning electron microscopy images. The findings of our study confirm that the releases from disposable N95 face masks pose a severe threat to freshwater microalgae, and the cascading effects would harm the aquatic ecosystems.

Assessing the Efficiency of Microalgae in the Removal of Salicylic Acid from Contaminated Water: Insights from Zebrafish Embryo Toxicity Tests

Microalgae-based water treatments for the removal of different types of pollution have been gaining considerable attention during the last few decades. However, information about microalgae potential in the removal of pharmaceuticals and personal care products (PPCPs) and the ecotoxicological outcomes is still limited. Therefore, in this work, we aimed at investigating salicylic acid removal from water by three different microalgae strains, namely Chlorella sorokiniana, Chlorella vulgaris and Scenedesmus obliquus. For such a purpose, photobioreactors were operated under batch and semi-continuous mode. Apart from determining the reduction in the concentration of salicylic acid attained by each strain, we used zebrafish embryo bioassays to assess the efficiency of microalgae to reduce its toxicity effects. S. obliquus was the strain that achieved the most significant decrease in the concentration and toxic effects of salicylic acid. Indeed, S. obliquus was able to rescue mortality and reduce abnormalities at practically 100%. The efficiency of C. sorokiniana and, especially, that of C. vulgaris were not so remarkable, indicating that the removal of SA and its toxic effects from water by microalgae is markedly strain dependent. The obtained results proved the importance of considering toxic effects for a more comprehensive evaluation of microalgae efficiency in the removal of PPCPs in view of an adequate selection for water treatment.

A chemical-free magnetophoretic approach for recovering magnetic particles in microalgae removal through magnetic separation

Magnetic separation can swiftly remove many substances (e.g., biomolecules, cells, and viruses) from water. In algal bloom mitigation and biomass dehydration, magnetic particles (MPs) with proper surface modifications could effectively attract and remove algae from the impaired water body. It has long been expected to recover and reuse magnetic nanoparticles or particles to reduce the algal removal cost and potential adverse effects on the environment. This study evaluated the use of a tunable magnetic field to remove algae using functionalized MPs coated with polymers: polyethyleneimine (PEI), chitosan (CTS), and cetyltrimethyl ammonium bromide (CTAB), whose recovery and reuse were examined. The results show that PEI-coated MPs and CTS-coated MPs at the coating density of 2.3 g-cationic polymers·g-MPs−1 achieved higher removal efficiencies of 88.61 ± 9.12% and 73.19 ± 0.37%, respectively, toward a model algal cell (i.e., Scenedesmus obliquus) within a 5-min separation time. In contrast, CTAB-coated MPs and pristine MPs exhibited lower removal efficiencies (47.46 ± 0.3% and 52.69 ± 0.44%, respectively). Furthermore, the removal efficiency of PEI-coated MPs was further improved to over 95% under pH 7, the highest magnetic field of 40 mT, and algogenic organic matter-free conditions. Adsorption kinetics and isotherm analysis revealed that chemical and physical interactions drive the adsorption of a monolayer of algal cells on the surface of magnetic particles. Atomic force microscopy and quartz crystal microbalance confirmed a strong adhesion force and rate between functionalized MPs and algae, which affect both algal removal efficiency and MPs recovery from algae-MPs aggregates. The extended Derjaguin−Landau−Verwey−Overbeek (EDLVO) theory predicted a strong attractive force between algae and cationic polymer-coated MPs, which supported the enhanced algal removal. Finally, almost 99% of the four MPs could be recovered from separated algae-MPs aggregates within 30 s under the strong magnetic field and exhibited excellent magnetic responsiveness and reusability in further separation cycles. This study establishes a foundation for coagulant-free algae removal and enables the potential sustainable separation processes.